In many internal combustion engines, in order to facilitate manufacturing, the engine casing is made of multiple components that are then fastened to each other. One of these components is the crankcase which, amongst other things, houses and supports the crankshaft for rotation therein.
One method of manufacturing the crankcase is casting. In order to facilitate the casting, the crankcase is typically made of two or more parts that are then fastened to each other. In crankcase made of two parts, the crankcase can be split along a plane containing the crankshaft axis, such as a horizontal plane, or along a plane that is perpendicular to the crankshaft axis. The latter provides some advantages with respect to the casting of the two portions of the crankcase.
Splitting the crankcase along a plane that is perpendicular to the crankshaft is often used for single cylinder engine as each portion of the crankcase forms one of the two supports necessary to support the crankshaft.
However, splitting the crankcase along a plane that is perpendicular to the crankshaft in a two-cylinder engine is more problematic. The plane along which the crankcase is split is preferably between the two cylinders. As such, the crankcase is split along the position where the crankshaft should be supported in the crankcase between the two cylinders.
In low power engines, one design consists in leaving the central portion of the crankshaft unsupported, and if necessary, providing a stiffer crankshaft to prevent crankshaft deformation. However, in high power engines, the crankshaft has to be supported between the two cylinders.
One solution consists in providing a separate central crankshaft support that is fastened to one of the two crankcase portions before fastening the two portions to each other. The fasteners are inserted perpendicularly to the plane along which the crankshaft portions are split (i.e. parallel to the crankshaft axis). Although this provides a support for the central portion of the crankshaft, it also causes torques to be applied to the crankcase. These torques are caused by forces transferred from the crankshaft to the crankshaft support during operation of the engine.
There is therefore a need for an internal combustion engine having a crankcase that is split along a plane that is perpendicular to the crankshaft and which provides support to a central portion of the crankshaft while limiting the torque being applied to the crankcase as a result of force transfer from the crankshaft.